Polymer crystallization method



United States Patent 3,327,021 POLYMER (IRYSTALLIZATION METHOD FrederickL. llinsbergen, Amsterdam, Netherlands, assignor to Shell Oil Company,New York, N.Y., a corporation of Delaware No Drawing. Filed May 25,1964, Ser. No. 370,081 Claims priority, application Netherlands, May 30,1963, 239,399 15 Claims. (Cl. 260-878) This invention relates to animproved crystallization method for the production of composites ofsolid crystalline polymers with crystallization modifying additives. Themethod leads to the production of modified polymers having improvedphysical properties.

The invention relates more specifically to an improvement in acrystallization method for the production of shaped articles and ofresin composites suitable for use in producing shaped articles, fromresins consisting substantially of crystallizable olefin polymers,particularly those produced from alpha-monoolefins in the presence oflow pressure catalysts of the Ziegler-Natta type. The invention is ofoutstanding advantage when used with isotactic polypropylene and will beillustrated largely with reference thereto,

Solid polypropylene is a new thermoplastic polymer which has recentlyachieved commercial importance. By use of appropriate conditions andcatalysts it can be produced in a sterically regulated form known asisotactic polypropylene. It is difficult if not impossible, topolymerize propylene to a polymer which has 100% isotactic structure.However, it is possible to produce, with commercially practicalcatalysts, polymers which have a high proportion of segments that arecompletely isotactic. A property which is associated with isotacticityof polypropylene is the capacity of a melt thereof to solidify incrystalline form.

Following conventionalterminology, reference to crystalline polymersmeans, unless the context indicates otherwise, solid polymers having ahigh degree of crystallinity, at least 50% as determined by X-rayanalysis or comparable methods. In general, polyproylene having acrystallinity of this order contains at most only a very smallproportion of material which is extractable in nonaromatic hydrocarbonsuch as gasoline boiling range hydrocarbons. Typically, the proportionof highly crystalline polypropylene which is extractable in boilingheptane or isooctane is less than 10% and usually less than 5%.Similarly, crystallizable polymers are those which have a moleculararrangement that enables them to solidify from a melt in a highlycrystalline structure. The general practice in the art is to refer tocrystalline or crystallizable polymer, rather than partially crystallineor partially crystallizable polymer even though olefin polymers of 100percent crystal structure are not known to exist. For example, acrystallinity of 70% is extremely high for isotactic polypropylene.Normally solid, crystalline polypropylene usually has a viscosityaverage molecular weight of at least about 40,000 and generally between100,000 and 1,200,000. For convenience the molecular weight is usuallyexpressed in terms of intrinsic viscosity. The intrinsic viscosity ofpolypropylene, measured in Decalin at 150 C., is generally between 1.0and 6 dL/g. but may be as low as 0.5 or less and as high as 10 or more.

Reference to polymers herein includes both homopolymers and copolymersunless the context indicates otherwise.

Crystalline polymers, in their usual form, have some outstandingly goodproperties and some undesirable ones. For example, desirable propertiesof highly crystalline polypropylene are high tensile strength andsubstantial hardness. One disadvantage of the usual forms of highlycrystalline polypropylene is a lack of transparency or clarity, whichshows up as haze in thin films and as translucency, decreasing toultimate opacity, in articles of progressively increased thickness.Another disadvantage of the usual forms of highly crystallinepolypropylene is a relatively low impact resistance. This handicaps theuse of isotactic polypropylene for making vessels or containers whichduring use may be subject to mechanical shock.

Polypropylene, like many other crystalline polymers, crystallizes from amelt in a form in which the individual crystals are associated inspheroid or ellipsoid bodies known as spherulites. Generally, clarityand some mechanical properties of articles made from polypropylene arebetter when the spherulites are relatively small.

It has been proposed to add a variety of materials to polyolefins toimprove polymer properties related to the rate of crystallite andspherulite growth.

It has now been found that alkali metal salts of cer' tain monosulfonicacids can be used as polymer additives to modify the crystallizationprocess and thereby provide substantial improvements in physicalproperties of solid polypropylene and in mechanical properties ofarticles produced therefrom, especially those properties which arerelated to crystallite and spherulite structure of the polymer. Similarimprovements of other crystallizable polymers may be obtained by use ofadditives of the same type. In many instances minute amounts of theadditives are extremely effective in modifying the crystallizationprocess and crystal structure.

The preferred materials which result in the production of solidpolypropylene of improved physical properties when used according tothis invention are sodium salts of sulfonic and aminosulfonic acids.Effective compounds of this type are identified in detail hereinafter.

The improvements of this invention are obtained when a compound such asone of said sodium salts of monosulfonic acids is present in dissolvedor thoroughly dispersed form in the polymer melt prior to the finalcrystallization thereof by cooling.

It is a specific object of this invention to provide an improvedcrystallization method for the production of composites of polypropylenewith crystallization modifying additives.

It is another specific object of this invention to provide articles ofcrystalline polypropylene which, by virtue of an improved crystalstructure, have improved mechanical properties and clarity.

It is another object to provide an improved crystallization method forthe production of composites of crystallizable polymers, such as linearpolymers of alphamonoolefins, with crystallization modifying additives.

Another object is to provide articles of crystalline polymers such aslinear polymers of alpha-monolefins which, by virtue of an improvedcrystal structure, have improved mechanical properties and clarity.

It is a major object of this invention to provide a novel method forcausing crystallizable polypropylene to crystallize with a very finespherulite structure.

Another object is to provide a novel method for causing crystallizablepolymers to crystallize with a very fine spherulite structure.

Other objects will become apparent from the following description ofthis invention.

According to this invention, solid crystalline polypropylene and othersimilar solid crystalline polymers of substantially improved physicalproperties are prepared by carrying out at least the finalcrystallization from a melt comprising the normally solid,crystallizable polypropylene or other polymer, together with a small,effective amount of at least one of said alkali metal salts ofmonosulfonic acids.

In another aspect, this invention comprises improved articles of solidcrystalline polypropylene or other similar solid crystalline polymers,prepared by crystallizing a melt of crystallizable normally solidpolypropylene or other similar polymer, containing a small, effectiveamount of at least one of said alkali metal salts of monosulfonic acids.

Several properties of the articles produced from normally solidcrystalline polymers according to this invention are improved thereby.The improvement will vary, depending on the particular polymer used,other additives used therewith, the particular compound selected fromthe group of compounds of the type of alkali metal salts of monosulfonicacids, and the conditions under which the final solidification of themelt takes place.

Generally, it is found that the spherulite dimensions in thecrystallized articles produce-d according to this invention aresubstantially smaller than they would be in an article produced inidentical manner from the same polymer but without using one of saidalkali metal salts of monosulfonic acids.

It is also generally found that the clarity of film or of thicker shapedarticles produced from compositions according to this invention issubstantially improved, compared to that of articles produced inidentical manner from the same polymer without one of said compounds ofthe type of alkali metal salts of monosulfonic acids, particularly whenthe final cooling step is under non-flow conditions.

The modulus of elasticity of polymer produced according to thisinvention generally is increased over that of the identical polymercrystallized in identical manner without one of said compounds of thetype of alkali metal salts of monosulfonic acids. Similarly, tensilestrength and other tensile properties are improved.

One of the advantages of this invention is that injection molding ofpolypropylene containing an alkali metal salt of monosulfonic acid inaccordance with this invention can be successfully carried out over amuch wider range of temperature and pressure conditions than in theabsence of crystallization modifying compounds. The area of a moldingdiagram for modified polymers, i.e., the area on the plot of cylindertemperature vs. ram pressure which covers satisfactory conditions, isgreater than that obtained with unmodified polymer.

Another advantage is that the mixtures according to this inventionsolidify at a higher temperature than those of identical polymers notcontaining said compounds of the type of alkali metal salts ofmonosulfonic acids. Hence, processing can generally be carried out in ashorter period of time. Another advantage of this invention is that itis possible to apply the process to highly crystalline polymers whichhave a relatively low melt index, allowing their being processed atlower temperatures.

It is further often found that impact resistance is greater in articlesproduced according to this invention than in those identically producedfrom identical polymer without one of said compounds of the type ofsodium salts of monosulfonic acids, particularly when the final coolingstep is under non-flow conditions.

In the compounds of the type of alkali metal salts of monosulfonicacids, the preferred metal used is sodium. Salts of lithium, potassium,rubidium and cesium, are similarly effective.

The sulfonic acids whose alkali metal salts are effective in accordancewith this invention are members of the group consisting of organicsulfonic and aminosulfonic acids. The salts are thus selected from thegroup consisting of compounds RSO M and 4- where M is an alkali metalcation, R is an organic group in which the SO M or NXSO M group isattached to a carbon atom, and X is hydrogen, halogen or a hydrocarbongroup.

In the salts described above, the sulfonate group or the amino sulfonategroup may be attached to a carbon atom of an aliphatic or of a cyclicgroup. The aliphatic group may contain one or more cyclic groups thatmay be attached to the carbon atom that also carries the sulfonate oramino sulfonate group, or to another carbon atom of the aliphatic group.Any of the cyclic groups attached to sulfur, nitrogen or carbon may bearomatic, cycloaliphatic or heterocyclic and may carry one or more alkylor alkenyl groups.

The aforesaid organic groups are preferably hydrocarbon groups of whichboth the aliphatic and the cycloali phatic representatives may besaturated or unsaturated and in which the unsaturated bonds may alsooccur in the rings.

The best results are generally achieved by applying alkali metal saltsof sulfonic acids that contain one or more cyclic groups and/or of whichthe carbon atom attached to sulfur or nitrogen is secondary or tertiaryand/ or another carbon atom attached to this carbon atom is tertiary orquaternary. The cyclic groups may be attached to the sulfur or nitrogenatoms or to a secondary, tertiary or quaternary carbon atom.

Of the acyclic salts the representatives having at most 12 carbons atomsare preferred. In the salts that contain cyclic groups the number ofcarbon atoms is preferably not more than 25.

The alkali metal salts used according to this invention also compriserepresentatives in which one or more of the carbon atoms carry asubstituent that is not a hydrocarbon group, for instance a halogenatom, a hydroxyl group, an amino group, an esterified carboxyl group oran ether group.

A wide and at present unexplained variability in effectiveness ofmembers of these broad groups of compounds has been observed. In a studyof the effect of sodium salts of a variety of these acids undercomparable conditions it was found that sodium sulfonates ofunsubstituted aromatic ring compounds, e.g., of benzene or naphthalene,and of compounds having only a single methyl substituent on the ring,i.e., toluene, all showed substantial nucleating activity. Sulfonates ofother lower monoand di-alkyl benzenes and naphthalenes may also berelatively highly effective, particularly where the alkyl group orgroups have from one to three carbon atoms per molecule. Compounds RSONa in which R is an alkyl group generally show poor nucleating activity,with the exception of a compound wherein R has the structure R being amet-hylgroup. However, substantial nucleating activity may also beobserved where R is ethyl or propyl.

Examples of salts that may be successfully used in the process accordingto the invention are the alkali metal salts of benzenesulfonic acid, ofalpha-toluenesulfonic acid, of para-toluenesulfonic acid, ofmeta-toluenesulfonic acid, of naphthalene-l-sulfonic acid, ofnaphthalene-Z-sulfonic acid, of phenylsulfamic acid and ofZ-methylpropane-Z- sulfonic acid.

Of the sulfonates and amino sulfonates applied according to theinvention it is generally the representatives that are colorless orsubstantially colorless that are preferred. By colorless orsubstantially colorless is meant that in the 1931 chromaticity chart ofthe Commission Internationale de laclairage (see Proceedings 8th Sessionof the Commission International de liz-clairage, Cambridge, England,September 1931, pp. 19-29) the position of the color is within thesaturation locus of 10% and that the brightness of the color acoordingto Color Coordinate Tables (Modified Adam Chromatic Value System) ascomputed by L. G. Glasser and D. I. Troy (J. Optical Soc. Am. 42 (1952)652) is between 0.00 and 30.00.

The alkali metal sulfon-ates, and also the alkali metal aminosulfonates, may, if so desired, be applied in the form of additioncompounds with carboxylic acids, preferably monocarboxylic acids, whichare acyclic-ally branched and/ or contain cyclic groups. In suchmonocarboxylic acids the acyclic and/ or the cyclic groups may besaturated or unsaturated, while suitable cyclic groups are aromatic,cycloaliphatic and heterocyclic rings.

The salts used are effective in low concentrations and are preferablyused in such low concentrations. Suitable concentrations are in therange from 0.01 or less to 5 percent by weight, based on the totalmixture. A suitable lower concentration limit is about 0.01 percent. Thecompounds are preferably employed in concentrations in the range from0.05 to 2 percent by weight. Although still higher concentrations may beused, no further benefit of the kind described is generally obtainedthereby.

The process of this invention may be carried out with a singlecrystallization modifying compound of the type described, or with amixture of two or more of such compounds.

If desired, other additives may be present in the olefin polymer.Crystallization modifying additives of other types may be added. Otheradditives, which are conventionally added, include antioxidants,stabilizers against ultraviolet radiation, and the like. They may beadded at any convenient stage of processing.

The present invention is advantageous when used with clear, unpigmented,unfilled polymers. However, the additives of this invention are alsocompatible with conventional fillers and pigments.

While this invention is most advantageous in providing improved articlesof crystalline polypropylene it may also be employed with advantage inimproving products made from other crystallizable hydrocarbon polymers,particularly alpha-olefine polymers and copolymers. Specific examplesare linear polymers of ethylene, l-butene, 4-methyl-l-pentene, and lhexene, crystalline copolymers of propylene with ethylene, l-butene andthe like, and crystalline polystyrene. Particularly desirableimprovements are obtained, for example, in block polymers, such as thoseconsisting predominantly of isotactic polypropylene having small amountsof ethylene, e.g., between 1 and percent, copolymerized therewith byblock polymerization. A preferred group are isotactic polymers ofalphamonoolefins having at least 3 and up to 8 carbon atoms permolecule. Polymers of alpha-monoolefins having from 2 to 4 carbon atomsare another preferred group. Polymers which can be improved according tothis invention have molecular weights and crystallinites in the rangedescribed above for polypropylene.

In one mode of practicing this invention, elastomeric polymer is addedto the polyolefin as a property-modifying additive, together with asulfonic acid salt. The addition of elatomers confers an improvement insome of the mechanical properties of crystalline polymers, e.g., theimpact strength. Suitable elastomers in general are predominantlyamorphous polymers having a glass transition point of less than 10% C.,measured according to ASTM test Dl043-5l. Suitable elastomers include asa preferred group rubbery copolymers of ethylene with alpha-olefins suchas propylene or l-butene, or other elastomeric olefin copolymers,including ter-p0lymers of two monoolefins and adiolefin, e.g.,dicyclopentadiene, and amorphous homopolymers of monoolefins, such asamorphous polypropylene. Other elastomers may be used, such as naturalrubber, polyisobutylene, butyl rubber, butadiene-styrene copolymers(SBR), butadiene-acrylonitrile copolymers (NBR), polybutadiene orpolyisoprene, particularly those of high cis-1,4 content, siliconerubbers, and the like. The elastomers which are added preferably haveWeight average molecular weights in excess of 50,000, suitably from 6100,000 to 500,000. Elastomer may be added in concentrations up to 35percent by weight, as a rule not more than 20 percent, and preferablybetween 3 and 15 percent. Use of sulfonic acid salts together withel-astomers provides polymer of improved properties, particularly lowtemperature (0 C.) impact resistance.

The polymers which are modified according to this invention are producedby polymerizing propylene or other suitable olefins by contact with ahighly stereospecific catalyst-system. A great variety of stereospecificcatalysts have been described in the literature. They are generallyspecies or modifications of the so-called Ziegler catalysts or Nattacatalysts.

The Ziegler type catalysts may be designated metal alkyl-reducible metalhalide type, and the Natta type catalysts preformed metal subhalidetype. This terminology is used, for example, in Polyolefin ResinProcesses by Marshall Sittig, Gulf Publishing Company, Houston, Tex.,1961. These well-known catalysts are the reaction products of halides,in order of preference chlorides and bromides, of transition metals fromsubgroups b of groups 4 and 5 of the Periodic Chart of Elements, i.e.,of Ti, Zr, Hf, V, Nb or Ta, with organometallic reducing agents in whichthe metal is from groups 1, 2 or 3. Preferred reducing agents areorganoaluminum compounds and particularly aluminum alkyls, includingaluminum alkyl halides. The most effective catalysts for the productionof isotactic polypropylene known to date are those prepared from certainforms of titanium trichloride and certain aluminum alkyls and aluminumalkyl halides.

In the production of crystallizable alpha-olefin polymers, the reactionmixture formed in the low pressure polymerization is treated todeactivate the catalyst, usually by contact with a polar compound suchas an alcohol and/ or hydrochloric acid, and is subsequently washed forremoval of at least a substantial portion of the catalyst residue. Theresulting polymer almost invariably contains at least traces of thecatalyst residue. Typically it may contain 50 parts per million (p.p.m.)of each of the catalyst components, calculated as the correspondingmetal. A carefully purified polymer may contain as little as 1 p.p.m. ofeach metal or less. The additives ofthis invention are useful inpolymers which contain relatively low amounts of the residue of saidcatalyst components, e.g., less than 50 ppm. calculated as thecorresponding metal, and especially in those containing from 0 to 10ppm. However, they provide equally good results when used in polymerscontaining large amounts of catalyst residue.

Various methods may be employed for introducing the additive of thisinvention into the polymer. It is generally preferred to add theadditive after the polymerization reaction has been completed, theactive catalyst has been killed and the predominant part of the catalystresidue washed out of the polymer. The additive may, for example, beadded to the washed polymerization slurry; the slurry is then dried anda dry mixture of additive and polymer is recovered. Alternatively,additive may be added to the dry polymer either when the polymer is inthe form of a powder flufi" or in the form of shaped pellets or thelike. It is also possible to add the additive to the crystallizablepolymer after it has been melted.

Another method of mixing the alkali metal salts with the crystallinepolymers is that in which the salts are dissolved in water, thesesolutions being mixed with the crystalline polymers, the salts thenbeing precipitated with the aid of a salting-out agent, for instanceacetone. The water and the salting-out agent are subsequently removed bymechanical means, for instance by filtration or centrifuging.

It is essential for effective results that a substantially homogeneousdistribution of the additive in the molten polymer be obtained prior tothe final crystallization of the polymer. To promote mixing of thepolymer and the additive it is best to apply mechanical mixing attemperatures at which the polymer has a relatively low viscosity, i.e.,a temperature exceeding the melting temperature of the polymer by from20 to 150 C. These conditions are particularly important when productsof greatly enhanced transparency are desired.

The additives may be present in the polymer melt in true solution or inuniform dispersion, e.g., as colloidal suspensions of liquids or solids.In one mode, extreme effectiveness is obtained by using them as solidsof from 0.01 to less than 1 micron diameter.

An essential step in the process according to this invention is thecooling of the polymer containing the sulfonic acid salts as additive atconditions resulting in a crystalline polymer structure. The finalcooling step in the production of a shaped article determines those ofits effective properties which depend on crystal structure. Whereas inthe absence of crystallization modifying additives slow cooling leads toformation of excessively large spherulites, and rapid cooling tends tolead to incompletely crystallized polymer, i.e., polymer having a lowerdegree of crystallinity than it is capable of achieving, the use ofadditives of this invention generally result in a polymer having a highdegree of crystallinity and a fine spherulite structure regardless ofwhether the cooling is carried out very rapidly or over a relativelylonger period of time. Rapid cooling can be carried out as quickly asheat conduction permits. This is, of course, a function of the geometryand heat removal capacity of each system. It can be completed in secondsin the production of film. Slow cooling may be carried out over a periodfrom several minutes to several hours.

Cooling of the polymer mixture can take place in any suitable apparatus.Cooling is usually carried out in conventional apparatus associated withthe production of shaped articles from olefin polymers.

The manner in which mixing takes place provides a uniform distributionof the crystallization promoting additive in the polymer. This uniformdistribution remains substantially unafifected during thecrystallization, both when crystallization progresses very rapidly andwhen there is a considerable temperature gradient, as in the cooling oflarge objects.

Shaped articles from product according to this invention may be, forexample, bars, sheets, films, tapes, granules, rods or flakes, molded orextruded large or small shapes or filament. Shaped articles according tothis in- -vention may be manufactured from the mixtures according tothis invention by casting, compression molding or injection molding;films may be obtained by blowing or by slit extrusion; filaments, bars,tapes and the like, may be obtained by extrusion. If desired these canbe reduced, by chopping, to the form of granules, chips or the like.Flaments can be stretched to obtain further improvement of properties.Other known methods of forming shaped polyolefin articles are equallyadapted to use with mixtures according to this invention.

The invention will be further described by reference to the followingexamples, which are not to be interpreted as limiting the invention butare merely intended to be illustrative of the invention.

EXAMPLE A number of experiments were carried out, in each case 2 mg. ofsodium salt of a sulfonic acid or amino sulfonic acid listed in thetable below being mixed with 200 mg. of polypropylene. The mixing waseffected in a highspeed vibrating ball mill.

The polypropylene had been prepared in a medium of technical isooctane,using a mixture of gamma-titanium trichloride and aluminum diethylchloride as the catalystforming components. This polymer had a meltindex of 1.0, an intrinsic viscosity (measured in decahydronaphthaleneat 135 C.) of 3.9 and a solubility in cold hexane of 6% by weight. Thepolymer also contained l6 l by weight of aluminum 20 10 by weight oftitanium. To a sample of each of these powder mixtures and to a linearlypolarized light that was caused by the preparations was measured. Thephotomultiplier was put in the eyepiece-tube and the light intensitystriking the photomultiplier was measured, both with crossed andparallel polarizers, a virtually parallel beam of light being applied asthe standard condition. Care was taken to ensure that the parts of thepreparations to be measured were free of orientation double refraction.

The results of the measurements are recorded in Table 1. Thedepolarization value A is the quotient of the intensity measured withcrossed polarizers and the intensity measured with parallel polarizers.It is expressed in parts per thousand (p.p.t.).

In the case of the preparation in which no alkali salt had beenincorporated the depolarization was about p.p.t. On this scale, thelowest values are indicative of the most effective nucleation effect.Values between 10 and 50 show that the product is a fairly goodnucleating agent.

It has been shown in studies with a variety of nucleating agents inpolypropylene that those for which measurements such as the above show asignificant nucleation effect also cause the improvements in mechanicalproperties described hereinbefore.

Table 1 Sodium salt of: A p.p.t. Benzenesulfonic acid 13Alpha-toluenesulfonic acid 13 P-ara-toluenesulfonic acid 17Meta-toluenesulfonic acid 30 Naphthalene-l-sulfonic acid l6Naphthalene-Z-sulfonic acid 20 Phenylsulfamic acid 30Z-methylpropane-Z-sulfonic acid 30 Z-naphthylhydrazinomethanesulfonicacid 25 p-Chlorobenzenesulfonic acid 40 I claim as my invention: 1. Themethod of producing polypropylene articles which comprises (A)dispersing in (a) polypropylene having a viscosity average molecularweight of at least 40,000 and a crystallinity of at least 50 percent, asmeasured by X-ray analysis (b) sodium benzene sulfonate in an amount inthe range 0.05 to 2 percent by weight, based on the polymer, (B) meltingthe resulting mixture, (C) shaping the melt into a desired shape, and(D)solidifying the melt by cooling it. 2. The method of crystallizing acrystallizable polyolefin which comprises (A) producing a melt of (a)normally solid, crystallizable polyolefin from 2 to 8 carbon atoms permolecule, containing (b) an effective amount, in the range from 0.01

to 5 percent by weight, of a substantially colorless crystallizationmodifying alkali metal salt of an acid selected from the groupconsisting of monosulfonic acids and mono-amino sulfonic acids, (B) andsolidifying said melt by cooling it. 3. A method according to claim 2wherein said polyolefin is polypropylene.

4. A method according to claim 2 wherein said polyolefin is a blockpolymer consisting predominantly of polypropylene and to a minor extentof other alphamonoolefin polymer.

5. The method of crystallizing crystallizable polypropylene whichcomprises (A) admixing (a) normally solid, crystallizable polypropylene(b) with an efiective amount, in the range of from 0.01 to 5 percent byweight, of a substantially colorless crystallization modifying sodiumsalt of an acid selected from the group consisting of monosulfonic acidsand mono-aminosulfonic acids;

(B) melting and mechanically Working the resulting mixture at atemperature of from 20 to 150 C. above the melting point of thepolypropylene, and

(C) solidifying the melt by cooling it.

6. A method according to claim 5 wherein said acid is =benzenesulfonicacid.

7. A method according to claim 5 wherein said acid isalpha-toluenesulfonic acid.

8. A method according to claim 5 wherein said acid ispara-toluenesulfonic acid.

9. A method according to claim 5 wherein said acid is a naphthalenesulfonic acid.

10. A method according to claim 5 wherein said acid is phenylsulfamicacid.

11. A method according to claim 5 wherein said acid is2-naphthylhydrazinomethanesulfonic acid.

12. A polypropylene composition of improved physical properties andreduced spherulite size, comprising (a) solid polypropylene having ahighly crystalline structure,

(b) containing an amount in the range from 0.01 to 5 percent by weightof a crystallization modifying alkali metal salt of an acid selectedfrom the group consisting of monosulfonic acids and mono-aminosulfonicacids,

(c) said salt having been dispersed in a melt of said polypropyleneprior to the fina-l solidification step. 13. A composition according toclaim 12 wherein said salt is sodium benzene sulfonate.

14. As an article of manufacture,

(a) shaped, crystalline polypropylene of improved physical properties,

(b) containing an amount in the range from 0.01 to 5 percent by Weightof a crystallization modifying alkali metal salt of an acid selectedfrom the group consisting of monosulfonic acids and mono-aminos-ulfonicacids;

(c) said salt having been dispersed in a melt of said polypropyleneprior to the final solidification step. '15. An article according toclaim 14 wherein said salt is sodium benzene sulfonate.

References Cited UNITED STATES PATENTS 3,207,735 9/1965 Wijga 26094.93,207,736 9/1965 Wijga 26094.9 3,207,939 9/1965 Wales 26094.9

JOSEPH L. SCHOFER, Primary Examiner.

LAWRENCE EDELMAN. Assistant Examiner.

2. THE METHOD OF CRYSTALLIZING A CRYSTALLIZABLE POLYDOLEFIN WHICHCOMPRISES (A) PRODUCING A MELT OF (A) NORMALLY SOLID, CRYSTALLIZABLEPOLYOLEFIN FROM 2 TO 8 CARBON ATOMS PER MOLECULE, CONTAINING (B) ANEFFECTIVE AMOUNT, IN THE RANGE FROM 0.01 TO 5 PERCENT BY WEIGHT, OF ASUBSTANTIALLY COLORLESS CRYSTALLIZATION MODIFYING ALKALI METAL SALT OFAN ACID SELECTED FROM THE GROUP CONSISTING OF MONOSULFONIC ACIDS ANDMONO-AMINO SULFONIC ACIDS, (B) AND SOLIDIFYING SAID MELT BY COOLING IT.4. A METHOD ACCORDING TO CLAIM 2 WHEREIN SAID POLYOLEFIN IS A BLOCKPOLYMER CONSISTING PREDOMINANTLY OF POLYPROPYLENE AND TO A MINOR EXTENTOF OTHER ALPHAMONOOLEFIN POLYMER.